SCX Switcher

A small Qt window and tray icon for sched_ext CPU schedulers on Debian 13. It shows which scheduler is running, starts, stops or switches one, picks a mode for it, and lets you decide whether it starts at boot.

It runs schedulers through scx.service and /etc/default/scx, which ship with the scx-scheds package from scx-bundler. It doesn't need scx_loader.

Requirements

• A kernel with CONFIG_SCHED_CLASS_EXT (Linux 6.12 or newer; Debian's own kernels have it)
• scx-scheds from scx-bundler
• polkit with pkexec and an authentication agent (every desktop session has one)

Build

Requires Docker.

./build.sh
sudo apt install ./out/scx-switcher_*.deb

The package is built in a clean debian:trixie container with dpkg-buildpackage and checked with lintian.

How it works

• The kernel says what runs. The app reads /sys/kernel/sched_ext/state, root/ops and enable_seq: every 2 seconds while the window is open, every 5 seconds in tray-only mode, and not at all otherwise. systemctl is only asked when something changes.

• One root helper makes changes. /usr/libexec/scx-switcher/scx-switcher-helper runs through pkexec:

  • start SCHED on|off [OPTIONS...] writes /etc/default/scx, restarts scx.service and waits for the kernel to confirm. If the scheduler fails, the previous one comes back.
  • boot on|off turns boot start on or off.
  • stop stops the scheduler now; boot start stays as it is.
  • stop-loader stops scx_loader when it holds the scheduler, since only one can run.

  It accepts only installed scx_* names and options made of letters, digits and - _ = . , : / +.

• Modes are option presets. They are the ones scx_loader ships. The window shows the exact command each one runs. Custom… takes your own options.

• Nothing starts at boot unless you tick "Start at boot". The app itself only starts at login if you tick "Start at login" in the tray menu. It then runs tray-only and never builds the window until you open it.

If a scheduler ever hangs the desktop, Alt+SysRq+S returns to the kernel default right away. The kernel also does this by itself when a scheduler stalls for too long.

License

MIT. Scheduler groups and descriptions follow sched-ext/scx (services/catalog.json and each scheduler's README); mode presets follow scx_loader.